What makes it interesting is just the fact that before the Wallis Simpson and abdication fiasco, the Princess Elizabeth in her early childhood was not thought likely to ever be Queen. Simply because Edward, the Prince of Wales at the time, was a young man and it was presumed that he would marry and have children of his own who would have precedence over everyone else. She was third in line but that was meaningless if Edward were to produce a whole brood of his own heirs.
The Wallis Simpson affair and abdication drastically changed things, but Elizabeth would still have been superseded if her parents, Prince Albert who became George VI and Queen Elizabeth the Queen consort, had had a son. But they didn’t, so by a series of historical quirks Elizabeth emerged first in line when George VI died in 1952.
Elizabeth II’s ascent is less remarkable than Victoria’s. She was the daughter of the 4th eldest son of George III. The 3 eldest left no surviving legitimate children and she had no brothers (or sisters). She ended up personally turning around the dearth of royal heirs.
George I was another that ascended oddly. He would have had 50 others ahead of him in line but they were Catholic and disqualified. He was the King Ralph of the day.
But at least those two were widely recognized as heirs and didn’t have to go to war or anything to succeed.
However, by the time Victoria was born it was pretty assured that at least two of the elder three sons of George III were not going to be producing heirs, so in some ways there were stronger grounds for thinking she had a real chance at inheriting.
(In fact, her birth was precisely BECAUSE of the hunt for an heir. In December 1817, George IV’s only daughter died shortly after giving birth to a stillborn son. Princess Charlotte of Wales had been the only legitimate grandchild of George III [who had 15 kids], so her death provoked a crisis. Her father the future George IV was still married to and estranged from the Princess of Wales, who was anyway past 50; the second brother Prince Frederick had been separated from his wife for more than two decades, and they’d never had children. Of the other five surviving brothers, three were past 40 and unmarried, one was illegally married, and the fifth was childless. Within a year, all three of the remaining unmarried brothers had a bride, and in the spring of 1819 there were four royal babies, of whom Victoria was the senior-most to survive.)
Stephen of Blois actually came from pretty far back. William II Rufus died unmarried, but both Robert Curthose and Henry I had legitimate sons ( William Clito and William Audelin respectively ) who would have superceded him if they hadn’t died first. Not to mention he was the fourth son in his family. One died young and the eldest was mentally incompetent. But even not counting his rival Mathilda, his older brother Theobaldstill should have preceded him. But Stephen was rather more popular in England proper and moved quicker to secure that power base while Theobald was still talking up supporters in Normandy ( including Stephen’s later great foe Robert of Gloucester who was on the continent at that time ). In the end Theobald reluctantly acquiesced to his brother’s coup de main.
It would have made for a great romantic success story as the friendly, brave and generous younger son with the very capable rich heiress wife climbed from semi-obscurity to the pinnacle of power ;). But sadly while Stephen was apparently all of those things, he was also easily led and vacillating with bad political judgement. So it all ended in a prolonged disaster.